It is already known to provide split leather or nonwoven needled fleece of natural or synthetic fibers with a dressing having a structured surface, for example a surface structured like leather grain. In this case, a liquid and wet compound forming the dressing is directly applied to the top surface of the split leather, for example by pouring, spreading, rolling, spraying or printing, or by a roller coating machine, and is then solidified by drying. For giving the dressing the structured surface of leather grain, the dressed split leather or nonwoven needled fleece of natural or synthetic fibers must be embossed after the liquid dressing compound has been dried or solidified. Such embossing of the split leather or nonwoven needled fleece of natural or synthetic fibers is effected in an embossing press under the action of heat and of a very high pressure. The structure of the split leather or nonwoven needled fleece of natural or synthetic fibers and of the dressing is thereby changed in an undesired manner. The thickness of the dressed split leather or nonwoven needled fleece of natural or synthetic fibers is not only reduced but the hardness and stiffness of the split leather or nonwoven needled fleece of natural or synthetic fibers is also increased. Furthermore, the vapor permeability, if any, of the dressing is reduced or destroyed, because during the embossing operation the pores existing within the dressing are again closed or destroyed, respectively, under the action of heat and pressure.
A substantial drawback of this known process resides in the fact that, for producing the dressing only thermoplastic materials deformable under the action of heat and pressure can be used, because otherwise subsequent production of the structured surface by subsequently embossing the solidified dressing would not be possible. Such thermoplastic synthetic plastics materials have, however, poorer properties than non-thermoplastic or less thermoplastic materials.
It is an additional drawback that production of the structured surface by embossing must be effected in a separate process step, which means that the dressed split leather or nonwoven needled fleece of natural or synthetic fibers must be further treated, i.e. must, as a rule, manually be inserted into an embossing press.
It is also known to apply the liquid dressing compound not directly onto the split leather or nonwoven needled fleece of natural or synthetic fibers but in several layers onto a support which is provided with an anti-adhesive coating and having a surface corresponding to the desired structure. The split leather or nonwoven needled fleece of natural or synthetic fibers is placed on the last layer while it is still wet and subsequently the thus dressed split leather or nonwoven needled fleece of natural or synthetic fibers is pressed within a roll press and/or is subjected to a vacuum treatment. In this manner, an undesired rigidifying and undesired increase in hardness and an undesired reduction of the thickness of the dressed split leather or nonwoven needled fleece of natural or synthetic fibers is substantially avoided, but the bond strength between the dressing and the split leather or nonwoven needled fleece of natural or synthetic fibers is reduced.
Further, it has already been proposed to first apply part of the dressing onto a supporting base and to allow solidification of the dressing and to apply a further part of the dressing onto one side of the split leather or nonwoven needled fleece of natural or synthetic fibers and to place this split leather or nonwoven needled fleece of natural or synthetic fibers with the dressing compound applied thereon, still in a wet state, onto the supporting base such that the side of the split leather being provided with the dressing rests on the solidified dressing applied to the supporting base and so that the dry side of the split leather or nonwoven needled fleece of natural or synthetic fibers having no dressing applied thereon shows in upward direction. The supporting base has, in this case, the negative shape of the desired surface of the dressing having the appearance of leather grain, so that, on drying the dressing compound under the action of low pressure, the dressing is given an appearance similar to that of leather grain. In this manner, the dressing is structured such that the thickness, the softness and the steam permeability of the split leather or nonwoven needled fleece of natural or synthetic fibers are not or are only scarcely changed. Dressed split leathers or nonwoven needled fleece of natural or synthetic fibers produced in such a manner thus are soft, supple and have an appearance and properties most similar to that of full-grain leather. The substantial drawback of this known procedure resides, however, in the fact that the split leather or nonwoven needled fleece of natural or synthetic fibers must manually be turned upside down immediately after the wet dressing compound has been applied for full contact between the supporting base, having a corresponding structure, at that side of the split leather or nonwoven needled fleece of natural or synthetic fibers which has been provided with the dressing compound and faces downwardly. In particular in connection with split leather or nonwoven needled fleece of natural or synthetic fibers of large area, manually turning over results in considerable difficulties and in great physical stress. Furthermore, air is included between the supporting base and the side of the split leather or nonwoven needled fleece of natural or synthetic fibers being provided with the dressing when manually turning over the split leather or nonwoven needled fleece of natural or synthetic fibers and placing same onto the supporting base, which substantially impairs the bonding strength of the dressing and the appearance of the dressing provided with the structure similar to leather grain at those areas where the air inclusions are present. This appearance is further impaired by damaging a still wet dressing when gripping the split leather or nonwoven needled fleece of natural or synthetic fibers for manually turning over same and by the necessity of subsequent shifting the split leather or nonwoven needled fleece of natural or synthetic fibers when it has not been placed on the supporting base in the correct position.